The invention relates to improvements in syringes, and more particularly to improvements in so-called single-use or non-reusable syringes.
A single-use syringe is designed in such a way that, once the flowable contents of its cylinder or barrel are evacuated through the needle in response to completion of forward stroke of its piston or plunger, the barrel cannot accept a second supply of flowable material and/or the plunger is incapable of expelling a second quantity of flowable material from the barrel. This is intended to prevent unauthorized persons, especially drug addicts, from reusing the syringe, a practice which is one of the primary reasons for the proliferation of AIDS and many other diseases, especially in countries or towns where the addicts seek to reuse discarded hypodermic syringes for intravenous injection of flowable drugs and/or the addicts share syringes with fellow drug users.
As a rule, a syringe comprises a cylindrical barrel the front end portion of which carries a needle and which confines a reciprocable plunger movable by a piston rod or shank which is accessible at the rear (proximal) end of the barrel. In order to prevent repeated use or uses of such syringes, the plunger is separated from the shank upon completion of its first forward stroke or the plunger cannot be retracted by the shank. In either event, the barrel cannot receive a second supply of a flowable substance. While a physician, a nurse or another trained and authorized person will desist from reusing a syringe, at least without a thorough and reliable sterilization of all parts which come into contact with the substance to be injected and/or with the body of a person who manipulates the syringe or who is to receive an injection, such practice is normally disregarded by many drug addicts so that the prevention of unauthorized use of discarded syringes is a high-priority project for medical and crime combating authorities all over the world.
European patent No. 0 438 453 B1 to Pickhard (published Aug. 18, 1983) discloses a syringe wherein the piston is provided with an axial passage closed by a transverse wall having a weakened portion which is destroyed in response to engagement by a projection provided in the front end portion of the barrel next to the fluid-receiving end of the needle and is intended to destroy the weakened portion while the shank is in the process of carrying out the last stage of its forward stroke. Alternatively, the weakened portion is provided on an insert which is confined in the plunger. Once the weakened portion is destroyed, the internal chamber or space of the barrel in front of the plunger begins to communicate with the atmosphere (by way of one or more radial ports in the plunger and by way of the open rear end of the barrel) so that a next-following retraction of the plunger cannot result in entry of additional flowable material into the barrel in front of the plunger.
It will be seen that the just described patented syringe cannot be reused provided that the first use results in actual destruction of the aforediscussed weakened portion which shares the movements of the plunger. However, a skilled hospital employee or a desperate or poor drug addict can readily acquire the skill which is required to avoid destruction of the weakened portion during the first use as well as during each subsequent use of the syringe. Such unauthorized manipulation is made possible in that a puncturing, a tearing or another mode of destroying the weakened portion necessitates the exertion of a relatively large force so that one seeking to reuse the syringe simply ceases to move the shank forwardly when such person detects or senses the need for the exertion of a greater force in order to continue the forward movement of the shank (i.e., of the plunger). Thus, the patented syringe can be reused as often as desired by the simple expedient of avoiding full depression of the shank and of the plunger toward the needle at the front end of the barrel of such syringe.
U.S. Pat. No. 5,000,735 (granted Mar. 19, 1991 to Whelan) discloses a single-use syringe wherein the plunger is made of rubber and is coupled to an enlarged forward end of the shank by a separately made support ring having breakaway tabs. The tabs are broken off, to thus terminate the motion transmitting connection, during the last stage of forward stroke of the shank relative to the needle-carrying barrel. This ensures that the plunger cannot be retracted away from the needle upon completion of the first and only injection carried out by the patented syringe. A drawback of this proposal is that several constituents of the patented syringe must be made of different materials as well as that the plunger, the shank and the support ring are discrete (separately produced) parts; this contributes to the manufacturing as well as to the assembly cost of such syringes.
U.S. Pat. No. 4,950,240 (granted Aug. 21, 1990 to Greenwood et al.) discloses a single-use hypodermic syringe which constitutes a modification of the syringe disclosed in the aforediscussed US patent to Whelan. The difference is that the shank is initially of one piece with a coupling which secures the plunger to the shank during the initial use of the patented syringe. The coupling is intended to be destroyed during such initial use. This syringe shares the drawbacks of the syringe disclosed in the patent to Whelan. In addition, the assembling of parts into the syringe of Greenwood et al. appears to be rather simple on paper but is quite problematic in actual practice, especially as concerns the ability of the coupling to withstand the stresses during assembly of the syringe, i.e., during the establishment of a breakable connection between the plunger and the shank in such a way that the connection can stand the developing stresses during admission of a flowable medicine or another injectable substance prior to as well as during the first use but to invariably break if one seeks to refill the barrel upon completion of the first use.
U.S. Pat. No. 5,163,908 (granted Nov. 17, 1992 to Lambert) discloses a fail safe composite hypodermic syringe wherein the plunger carries a conical extension bearing a sphere which is initially coupled to pin-shaped segments at the inner side of a hollow shank. Such connection is terminated upon the intended first and only use of the patented syringe. This syringe shares the drawbacks of syringes which are disclosed in the patents to Whelan and Greenwood et al. Moreover, the plunger and the shank of this syringe cannot be made by resorting to simple and inexpensive methods, e.g., to mass production in an injection molding or extruding machine.
Published European patent application Serial No. 0 409 134 A1 of Sempere Escudero (published Jan. 23, 1991) discloses a single-use syringe wherein the plunger is initially coupled to the shank by a breakable annular membrane which is to be destroyed in response to first retraction of the shank, i.e., upon completion of a first injection of flowable material into a living being. To this end, the plunger is captured between a pair of stops which are provided at the inner side of the barrel close to the needle. The drawback of this syringe is the same as that of the syringe disclosed in the aforediscussed European patent No. 0 438 453 B1 to Pickhard, i.e., a skilled nurse or addict can avoid capturing of the plunger between the internal stops of the barrel by the simple expedient of terminating the forward progress of the plunger before the shank reaches its foremost or innermost position.
U.S. Pat. No. 4,863, 427 (granted Sep. 5, 1989 to Cocchi) discloses a single-use syringe wherein a retraction of the plunger subsequent to the first use of the syringe is prevented in that the plunger becomes separated from the reciprocable shank in response to destruction or deactivation of a coupling between such parts, or in response to the establishment of communication between the chamber in front of the plunger and the atmosphere, not later than when the plunger completes its first forward stroke. FIGS. 1 to 3 of this patent show two embodiments of a further modification which appears to be problematic even on paper but appears to be plainly devoid of any utility in actual practice.
An object of the present invention is to provide a single-use syringe which is more reliable (less likely to be used more than once) than heretofore known single-use syringes.
Another object of the invention is to provide a novel and improved destructible connection or coupling between the piston or plunger and the piston rod or shank of a syringe.
A further object of the instant invention is to provide a single-use syringe which is more reliable and less expensive than heretofore known single-use syringes.
An additional object of the invention is to provide a novel and improved plunger for incorporation into a single-use syringe.
Still another object of the present invention is to provide a novel and improved shank for incorporation into a single-use syringe.
A further object of this invention is to provide a novel and improved method of making a plunger-shank combination for incorporation into a single-use syringe.
Another object of the invention is to provide a single-use syringe wherein a renewed introduction of a flowable substance into the barrel is prevented in a novel, improved and reliable manner.
An additional object of the invention is to provide a single-use syringe which can be employed as a superior substitute for syringes disclosed in the aforediscussed patents and patent applications.
The invention is embodied in a single-use syringe which comprises an elongated tubular barrel having an open first end portion and a second end portion which is arranged to support a needle (e.g., a needle which is detachable from the barrel), a plunger which is reciprocably received in and defines with the barrel a variable-volume fluid-receiving chamber adjacent the second end portion of the barrel, an elongated shank having a distal end adjacent the plunger and a manually shiftable proximal end at the first end portion of the barrel, and a coupling which connects the plunger with the distal end of the shank. In accordance with a feature of the invention, the coupling includes an array of preferably equidistant circumferentially spaced-apart breakable spokes each of which is or can be of one piece with the plunger as well as with the distal end of the shank.
The arrangement is or can be such that the spokes break in response to movement of the shank toward the second end portion of the barrel to thus cause the plunger to expel fluid from the chamber through the needle at the second end portion of the barrel. Upon breakage of the spokes, the distal end of the shank is movable (a) against the plunger to move the plunger toward the second end portion of the barrel and/or (b) away from the second end portion of the barrel and away from the plunger, i.e., the plunger cannot be used to draw a second supply of flowable material through the needle and into the chamber.
In a presently preferred embodiment of the improved syringe, the plunger is provided with a recess which is arranged to receive the distal end of the shank upon breakage of the spokes in response to further movements of the shank toward the second end portion of the barrel. The recess can constitute a relatively shallow circular blind bore or hole or depression having a diameter greater than that of the distal end of the shank so that such distal end can enter the recess (i.e., the shank can move relative to the plunger in a direction toward the needle) upon breakage of the spokes.
It is within the purview of the invention to provide the plunger with projections, e.g., with at least one for each of the spokes and each integral with the respective spoke at least prior to breakage of of the spokes. The projections are or can be of one piece with the plunger and can extend in the barrel in a direction away from the second end portion of the barrel.
The distribution of the spokes can be such that each spoke extends from the shank at least substantially radially outwardly toward the plunger.
The distal end of the shank can be provided with a disc, and the spokes can extend at least substantially radially of and from the disc toward the plunger.
At least one of the spokes can be provided with surfaces which converge toward each other radially outwardly of the shank and toward the plunger.
The areas of contact of the spokes with the plunger can be smaller than the areas of contact of the spokes with the distal end of the shank.
The spokes can form part of a hollow conical frustum.
In accordance with still another modification, the plunger is spaced apart from the distal end of the shank and the spokes are elongated and extend longitudinally or substantially longitudinally of the shank between the distal end of the shank and the plunger.
The aforementioned recess of the plunger can be bounded by a conical surface which is connected with the spokes at least until the spokes are caused to break.
In accordance with an additional modification, the plunger includes a first portion which is connected with the distal end of the shank by the aforementioned spokes, and a second portion which at least partially surrounds the first portion at sealingly engages the barrel. The second portion of the plunger can resemble or constitute a cup having a cylindrical sidewall which surrounds the first portion.
The internal surface of the barrel can be configurated in such a way that it includes a first portion offering a relatively low first resistance to movements of the plunger toward and away from the second end portion of the barrel, and at least one second portion which offers a greater second resistance to such movements of the plunger. The at least one second portion of the internal surface can be provided on an annular internal constriction of the barrel; such internal constriction fully or at least partially surrounds the shank. For example, the constriction can include a circumferentially complete collar extending radially inwardly from the first portion of the internal surface.
The barrel can be provided with a cylindrical internal surface along which the plunger is slidable toward and away from the second end portion of the barrel. Such internal surface can include an at least substantially frustoconical portion which is adjacent to and tapers toward the second end portion of the barrel and serves to offer a progressively increasing resistance to movement of the plunger toward the second end portion of the barrel.
The barrel can constitute a one-piece extrusion. Analogously, the shank, the spokes and at least a portion of the plunger can also constitute a one-piece extrusion.
Furthermore, at least a portion of the plunger can consist of a resilient material and at least a portion of the shank can have a substantially or exactly cruciform cross-sectional outline.